The quality of climate data is critical for reliable simulations of spatial and temporal variations in the carbon budget. To examine the quality of the new dataset produced by the JMA reanalysis project (JRA-25), we applied JRA-25 data as well as data from the established climate datasets NCEP-R1, NCEP-R2, and ERA40 to the terrestrial ecosystem model Sim-CYCLE and compared the result. Using each of the datasets, we conducted global simulations for the period 1979-2001 and investigated the spatial and temporal patterns of plant uptake and the net ecosystem budget of carbon. The JRA-25 dataset provided pertinent land surface conditions with respect to solar radiation, temperature, and precipitation, resulting in moderate simulation results of terrestrial productivity and the carbon budget. Unusual conditions of the JRA-25 resulted in different regional carbon budgets such as the Amazon basin and global budgets in a few anomalous years.